BUG #16539: About pg_logdir_ls() function and pg_ls_logdir()function

The following bug has been logged on the website:

Bug reference:      16539
Logged by:          yanliang lei
Email address:      leiyanliang@highgo.com
PostgreSQL version: 12.1
Operating system:   CentOS7.7
Description:

In the https://www.postgresql.org/docs/12/adminpack.html，there is a function
which name is  pg_logdir_ls() ，but there is no this function name from psql
query（the following query），why？

postgres=# \df pg_ls_logdir
                                                        List of functions
   Schema   |     Name     | Result data type |
Argument data types                            | Type 

------------+--------------+------------------+---------------------------------------------------------------------------+------
 pg_catalog | pg_ls_logdir | SETOF record     | OUT name text, OUT size
bigint, OUT modification timestamp with time zone | func
(1 row)

postgres=# \df pg_logdir*
                       List of functions
 Schema | Name | Result data type | Argument data types | Type 
--------+------+------------------+---------------------+------
(0 rows) ---->>>there is no pg_logdir* function！！！

postgres=# select version();
                                                 version
                            
---------------------------------------------------------------------------------------------------------
 PostgreSQL 12.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)

postgres=#